CORONAL MASS EJECTIONS

A coronal mass ejection (CME) is the eruptive release from the Sun's outer atmosphere (the corona) of a large cloud of plasma containing several million tons of material in which is embedded solar magnetic fields. These eruptions occur from regions in the Sun in which the magnetic field is closed but which suddenly suffers an extremely energetic disruption. Their speed varies from a few hundred km/sec up to around 1500 km/sec. The frequency of CME's has been observed to vary from once every few days to several times a day.

• As the plasma cloud moves out from the Sun it expands so that the volume:
  
  V ~ R²
• The linear dimensions (L) of the cloud scale as the cube root of the volume, so the length or diameter of the cloud varies as:
  
  L ~ R^2/3
• The magnetic field (B) which is 'frozen in' and thus carried along by the plasma is given by:
  
  B ~ 1 / V
  and thus:
  
  B ~ 1 / R²

Some typical values for a CME:

   Solar Distance           Diameter        Magnetic Field
    R(million km)         L(million km)      B(nanoTesla)

     10 {15 solar radii}       1.0               1000
     20                        1.6                250
     30                        2.0                111
     40                        2.5                 63
     50                        2.9                 40
     60 {Mercury orbit}        3.2                 28
     70                        3.6                 20
     80                        3.9                 16
     90                        4.2                 12
    100                        4.6                 10
    110 {Venus orbit}          4.9                  8
    120                        5.1                  7
    130                        5.4                  6
    140                        5.7                  5
    150 {Earth orbit}          6.0                  4

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